65 research outputs found
Effective Hamiltonian with holomorphic variables
The pure-quantum self-consistent harmonic approximation (PQSCHA) permits to
study a quantum system by means of an effective classical Hamiltonian. In this
work the PQSCHA is reformulated in terms of the holomorphic variables connected
to a set of bosonic operators. The holomorphic formulation, based on the
olomorphic path integral for the Weyl symbol of the density matrix, makes it
possible to directly approach general Hamiltonians given in terms of bosonic
creation and annihilation operators.Comment: Proceedings of the Conference "Path Integrals from peV to TeV - 50
Years from Feynman's paper" (Florence, August 1998) -- 2 pages, ReVTe
Effective Hamiltonian with holomorphic variables
The pure-quantum self-consistent harmonic approximation (PQSCHA) permits to
study a quantum system by means of an effective classical Hamiltonian -
depending on quantum coupling and temperature - and classical-like expressions
for the averages of observables. In this work the PQSCHA is derived in terms of
the holomorphic variables connected to a set of bosonic operators. The
holomorphic formulation, based on the path integral for the Weyl symbol of the
density matrix, makes it possible to approach directly general Hamiltonians
given in terms of bosonic creation and annihilation operators.Comment: 11 pages, no figures (2nd version: few mistakes fixed in Sects. IV-V
Effective potential approach to quantum dissipation in condensed matter systems
The effects of dissipation on the thermodynamic properties of nonlinear
quantum systems are approached by the path-integral method in order to
construct approximate classical-like formulas for evaluating thermal averages
of thermodynamic quantities. Explicit calculations are presented for
one-particle and many-body systems. The effects of the dissipation mechanism on
the phase diagram of two-dimensional Josephson arrays is discussed.Comment: 7 pages, 5 figures, to appear in the Proceedings of Nonlinearity,
Integrability And All That 20 Years After Needs 7
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